In the transportation industry and particularly in the trucking industry, properly inflated pneumatic tires are essential. In the trucking industry, eighteen wheelers are the standard of the industry with two tires on each side of each axle. The tires must support significant loads and duel tires provide redundancy so that failure of a single tire on either side of an axle does not totally disable the vehicle. It is important to test the state of inflation of truck tires at periodic intervals. Current U.S. regulations by the Department of Transportation (DOT) require inflation inspection of all tires on a truck every three hours of operation when carrying standard cargo and every two hours when carrying hazardous materials.
It has been found that the major cause of truck tire failures and blowouts, is due to damage caused by heat buildup from running the tire when it is under-inflated. Thus, it is extremely important to periodically check the inflation of truck tires. At fueling stations and truck repair facilities or fleet service yards, air pressure testing can be conducted by applying an air gauge to the valve of each tire. Tire pressure testing using air pressure gauges is less convenient along the road at poorly lighted areas. This procedure, if properly conducted with accurate air pressure gauges can produce reliable results; but such testing with air pressure gauges is time-consuming. In the case of eighteen wheelers, the use of air pressure gauges to test all the tires can take at least four to six minutes for an eighteen wheeler without valve stem covers and eight to thirteen minutes if there are valve stem covers. For triple trailers or nonstandard trailers where the number of wheels is greater, sometimes up to 26 wheels or more, the time required for air pressure gauge testing increases to as much as twenty minutes or more. During a typical trip with a team of two drivers requiring thirty hours of travel time, for example, from Houston to Los Angeles, compliance with DOT regulations requires ten stops (fifteen stops for hazardous material transport). The loss of travel time for such a trip may be anywhere between forty minutes and more than three hours for each trip carrying standard freight, and between one hour and five hours for each trip carrying hazardous freight ("HAZMAT").
As an alternative to air pressure gauge testing for determining proper inflation of truck tires, kicking the tires or striking the tires with sticks, pipes, bars, and hammers is sometimes attempted. The concept for such prior devices was that the impact action against the tire produced a noise or feel that could be vaguely indicative of tire inflation. Properly inflated truck tires are typically inflated to about 100 PSI. Some operators consider inflation over 60 PSI to be acceptable and anything less than 60 PSI to be "flat". It has been found that significant damage and expenses can result when tires are run at less than about 80 PSI. Previous striking sticks, pipes, bars, and hammers cannot adequately distinguish between tires inflated at 100 PSI and those at 60 PSI. Such devices produced inadequate and inconsistent results for a variety of reasons. Even if a striking device has sufficient weight, the results are still inadequate because of inconsistencies of the striking impact "footprint". In the case of a standard hammer the "footprint" or impact area may be too large when the face of the hammer hits the tire tread or too small when the edge of the face hits the tire. A ball-peen hammer requires that the angle or position of the hammer head be identical for every blow; it is difficult at best to maintain a consistent angle with respect to all the tires whether inside, outside, left, right, forward, and back tires. All must be tested. In the case of pipes, sticks and bars, the results of striking the tire can be completely different depending upon the angle of impact whether the impact is at the corner at the end of the cylindrical-shaped tool or on the side of the shaft.
Time constraints, delivery schedules, and tiredness encourage the professional truck driver to complete the required testing as quickly as possible; yet, inadequate tools previously existed for rapid and accurate tire testing. Still, under-inflation is a primary reason for tire failure and blowouts. This results in potentially hazardous conditions ranging from potential loss of control of the truck, to producing road hazards for other motorists, and to damaging electrical lines, hydraulic hoses, mud flaps, and other vulnerable parts of the truck trailer. This also results in added costs. Combination downtime at the side of the road or even at a service facility and the time and effort for replacement of the tire and the expense of the tire replacement are all costs that result from tire failure. It has been found that truck drivers and trucking companies with well-maintained trucks may still experience an average of one blowout a week as a result of excessive wear due to heat from under-inflated tires.